G Protein Coupled Receptors
G proteins are heterotrimeric proteins which are capable of conveying information from cell surface receptors to internal components of a cell. Those internal components include components regulating gene transcription, protein structure and activity, cell conformation and movement, cell metabolism, nerve impulse transmission, cardiac function, olfaction, vision, and many other cellular processes that are responsive to external stimuli. The cell surface receptors that sense extracellular compounds or conditions and convey this signal to G protein include a class of integral membrane proteins commonly designated G protein coupled receptors (GPCRs). Crudely summarized, GPCRs exist in one of two states—active and inactive (see, e.g., Gether et al., 1998, J. Biol. Chem. 273:17979-17982).
In its active state, a GPCR is able to interact with a G protein and activate that G protein (by promoting exchange of GTP in place of GDP on the alpha subunit of the G protein and subsequent dissociation of the alpha subunit from the beta and gamma subunits of the G protein). In many instances, time-dependent decrease of the cellular response to an external signal normally detected by a GPCR/G protein pair occurs, despite the continued presence of the signaling ligand or condition. This attenuation of GPCR-/G protein-mediated signaling is commonly designated desensitization, and has well recognized importance in physiological and pharmacological settings.
One mechanism by which GPCR desensitization can occur is commonly referred to as homologous desensitization (i.e., desensitization of only an activated GPCR, rather than others) and involves phosphorylation of the GPCR by an enzyme of the class generally known as GPCR kinases (GPCRKs). GPCRK-catalyzed phosphorylation of an activated GPCR can inhibit signaling mediated by the GPCR, and also promotes association of the phosphorylated GPCR with an arrestin protein. Arrestin binding prevents association of a GPCR with its corresponding G protein, halting signaling. Arrestin binding also promotes internalization and sequestration of the GPCR, leading to long-term desensitization of the GPCR.
Numerous GPCRKs have been described, and many more are believed to exist. In view of the widespread and critical nature of GPCRK activities in normal and pathological physiological processes, a need exists for identification of further members of this protein family. The present invention satisfies this need by providing a novel human GPCRK, designated 69087.
Nuclear Signaling Proteins
Regulation of gene transcription in eukaryotic cells in response to cellular stimuli (e.g., cell cycle or nutritional state indicators) or environmental stimuli (e.g., heat, presence of an attractant, or presence of a surface such as that of a neighboring cell) requires transduction of a signal across the nuclear membrane and interaction of a protein with the gene.
A significant mechanism by which nuclear transmembrane signaling can occur is by alteration of the structure of a nuclear transmembrane protein. Such alteration can be effected by binding of a ligand (e.g., a protein, a hormone, or a steroid) with the nuclear transmembrane protein on the cytoplasmic face of the nuclear membrane. Following binding of the ligand with the protein, the conformation of the protein is altered on the nuclear face of the nuclear membrane, thereby altering the properties exerted by the nuclear transmembrane protein on the contents of the nucleus. By way of example, ligand-bound nuclear membrane protein can be able to bind with a nuclear protein that is not able to bind with the non-ligand-bound form of the nuclear membrane protein (or the reverse).
Intranuclear signaling can occur by interaction of a protein with another protein (e.g., a DNA-associated protein, a component of the transcriptional apparatus, or a nuclear transmembrane signaling protein), with a nucleic acid, or with both. A variety of intranuclear signaling proteins are known in humans, including, for example, transcription factors, enhancers and repressors of transcription, recombination-modulating proteins, and modulators of these proteins.
Nuclear transmembrane signaling and intranuclear signaling (individually and collectively designated “nuclear signaling” in this disclosure) are involved in a variety of physiological and pathophysiological processes. For example, nuclear signaling can enhance or inhibit expression of a gene in response to the occurrence or presence of an environmental stimulus. Nuclear signaling can also mediate interconnections between cytoskeletal components and the nuclear membrane or a component of the nuclear contents (e.g., with a centromere or with a particular region of a chromosome). Interaction of a nuclear signaling protein with a cytoplasmic or nuclear component can also modulate the properties of the nuclear membrane (e.g., the porosity of the membrane or the ability of a particular compound to traverse the membrane).
Numerous nuclear signaling proteins have been described, and many more are believed to exist. In view of the widespread and critical nature of nuclear signaling protein activities in normal and pathological physiological processes, a need exists for identification of further nuclear signaling proteins. The present invention satisfies this need by providing a novel human nuclear signaling protein, designated 15821.
Mitogen-Activated Protein Kinase Phosphatases
Protein phosphorylation, for example at serine, threonine, and tyrosine residues, is a key regulatory mechanism for a variety of cellular processes. For example, protein phosphorylation is involved in regulation of cell growth and differentiation, entry of cells into the cell cycle and their progression through the cell cycle, mitogenesis, cell motility, cell-to-cell interactions, cell metabolism, gene transcription, expression of normal and aberrant immune responses. The extent of protein phosphorylation influences cell signaling processes, including those signaling processes mediated by G proteins and their corresponding receptors.
Protein phosphorylation is influenced primarily by enzymes of two types, namely protein kinases (PKs) and protein phosphatases (PPs). PKs catalyze addition of a phosphate moiety to a protein amino acid residue (generally a serine, threonine, or tyrosine residue), and PPs catalyze removal of such moieties. The catalytic activities of PKs and PPs are, in turn, influenced by the state of the cell and the environment in which it finds itself.
Phosphorylation of amino acid residues by a PK generally manifests itself in the form of faster cell growth, metabolism, or division, as greater cell motility, or in the form of higher gene transcription, although certain physiological processes are inhibited by protein phosphorylation. De-phosphorylation of amino acid residues by a PP, by contrast, generally manifests itself as slower (or halted) cell growth, division, or metabolism, as lower cell motility, or in the form of lower gene transcription. PK/PP-modulated protein phosphorylation is also involved in carcinogenesis.
Among the PKs that have been described are a class of PKs alternatively designated mitogen-activated protein kinases, MAP kinases, MAPKs, extracellular signal-regulated protein kinases, and ERKs. MAP kinases are the terminal enzyme in a three-kinase cascade. MAPKs are activated by phosphorylation catalyzed by MAPK kinase enzymes (MAPKKs), which in turn are activated by phosphorylation catalyzed by MAPKK kinase enzymes (MAPKKKs). Ability of a cell to activate a variety of MAPKs permits the cell to respond to a variety of extracellular signals with a physiological response that is appropriate for the state of the cell. A single MAPK enzyme can phosphorylate multiple other proteins within the cell, including, for example, other PKs, transcription factors, cytoskeletal proteins, and other enzymes. De-phosphorylation of MAPKs is a significant aspect of cell signaling, and is catalyzed by proteins designated MAPK phosphatases (MAPKPs). The phosphorylation state of MAPKs can be regulated in a cell by the opposing actions of MAPKKs and MAPKPs.
In view of the widespread and critical nature of MAPK-mediated signaling, and the corresponding significance of MAPKP activities in normal and pathological physiological processes, a need exists for identification of further members of the MAPKP protein family. The present invention satisfies this need by providing a novel human MAPKP designated 15418.